1. Field of the Invention
The present invention relates to an image pickup apparatus including different types of focus detection units.
2. Description of the Related Art
Conventionally, as focus detection methods of an image pickup apparatus, a phase difference detection method which detects a pair of image signals obtained from a light beam that has passed through different pupil regions of an optical system and a contrast detection method which uses a contrast component of an image signal have been known. In addition, as one of the phase difference detection methods, an imaging plane phase difference detection method has been known which performs focus detection by the phase difference detection method by using an output from an image pickup element.
Japanese Patent Laid-Open No. (“JP”) 2001-083407 discloses, as a focus detection method adopting the imaging plane phase difference detection method, a configuration in which each of a plurality of photodiodes (hereinafter, referred to as “PDs”) provided to its corresponding micro lens receives light from pupil regions different from each other. Such a configuration enables focus detection by the phase difference detection method by comparing outputs of two PDs.
The image pickup apparatus has been known which allows a user to select an AF method from a plurality of AF methods such as the phase difference detection method and the contrast method. JP 2012-118154 discloses a configuration which selects the contrast detection method using a wobbling lens because narrowing down an aperture stop results in a decrease in accuracy of autofocusing (AF method) by the phase difference detection method.
In the focus detection by the imaging plane phase difference detection method, some lenses suffer from a displacement of an in-focus position (hereinafter, referred to as a “best focus (BF) shift”) which is caused by an aberration and a chromatic aberration of an object light beam of a shot image and that of the focus detection. Due to this drawback, some interchangeable lenses designed to be mounted on an image pickup apparatus may not be able to satisfy an in-focus accuracy allowable as a still image. If an image pickup apparatus stores a correction values (hereinafter, referred to as a “best focus (BF) correction value”) designed to correct the BP shift for every type of interchangeable lens, an extremely large amount of data capacity is required. Furthermore, in order to make it possible to correct the BF shift for interchangeable lenses to be released in the future, firmware updating and other measures are required and this approach is inefficient.